36 



The Waterlilies. 



length of each adventitious root. Branches are given off from it at right 

 angles and pass straight out through the cortex to the side rootlets. 

 Where the root joins the stem, the root-bundle passes in and bends 

 sharply backward (away from the stem apex) and runs more or less 

 obliquely into the plexus of bundles of the stem. In N. odorata the bundles 

 of all of the roots from a single leaf-base unite in the peripheral region of 

 the stem into one strong trunk (Fig. 10) ; the appearance of a pith in the 

 midst of this trunk in N. alba candidissima gives rise to the " root-bearing 

 stele" of Gwynne-Vaughan (1896 b). In N. lotus each root-bundle 

 passes in separately and breaks up into a number of branches before 

 joining the plexus of the stem. It is notable that there is no direct 



connection between the bundles of any leaf and 

 the roots which spring from its base, close as their 

 proximity is. 



The innumerable small rootlets which cover 

 the main roots seem to repeat entirely the struc- 

 ture of the latter. The vascular system (in N. 

 elegans x zanzibariensis) is hexarch, with uniseriate 

 pericambium and a tiny central pith ; endodermis 

 and endo-cortex are uniseriate and distinct ; the 

 meso-cortex has only one or two series of very 

 small and irregular air-canals ; hypodermis and 

 epidermis occur as above described. 



The rudiments of roots are laid down below 

 the bases of the petioles at a very early period. 

 In a strong rhizome of N. odorata a leaf bud less 

 than 0.3 cm. long, including the petiole, had four subtending roots already 

 laid down in the tissues of the cushion just below it ; the posterior two of 

 these had the root-cap well defined and had destroyed some of the 

 overlying cortical cells of the stem. After this time, however, their 

 development is very slow ; at the base of a petiole over 8 cm. long the 

 root apices had just penetrated the epidermis, but were still concealed in 

 the short pubescence of the leaf-cushion, No pericambial tissue has yet 

 been distinguished in Nymphaeaceous stems for the source of adventitious 

 roots. 



Reference has been made to cell-multiplication in the apex of growing 

 roots, and to the early origin of the air-canals. These canals are at first 

 surrounded by six cells. Between every two of these another cell is cut 

 off, giving one at each angle of the canal, and one on each side (Fig. 1 1 b). 



Fio. 10. Vascular bundles of 

 the roots of N. odorata. Longitu- 

 dinal section of leaf-base. 



